2. Mendelâs Work
ď¨ Mendel experimented with thousands
of Pea plants looking at their different
traits to understand the process of
heredity. His discoveries form the
foundation of genetics.
ď¨ Heredity âthe passing of physical
characteristics from parents to
offspring
ď¨ Trait- each different form of a
characteristic
ď¨ Genetics â the study of heredity
3. Mendelâs Experiments
ď¨ Flowering Plant anatomy
ď¨ Pistil â produces the female
ď¨ sex cells or eggs
ď¨ Stamens â produce pollen which contains
the male sex cells or sperm
ď¨ Fertilization is when the egg and sperm
join forming a new organism
ď¨ In plants the pollen must reach the pistil
for fertilization to occur. This is called
pollination
4. Pollination
ď¨ Pea plants usually self-
pollinate. The pollen from their
stamens lands on the same
plants pistils.
ď¨ Mendel developed a method
to cross-pollinate pea plants.
He took pollen from one pea
plant and brushed it into the
pistil of another.
5. Crossing Pea Plants
ď¨ Mendel crossed plants with
contrasting traits
ď¨ Ex. Tall plants with short
plants
ď¨ Started with purebred plants
a purebred organism is one
who is the offspring of many
generations of that have the
same trait
6. The F1 Offspring
ď¨ Mendel crossed
purebred tall with
purebred short
Parental (P) generation
ď¨ Tall x short
ď¨ Offspring from the
cross are called F1
(filial)
ď¨ All F1 offspring were
tall
7. F2 offspring
ď¨ When F1 were full
grown, Mendel
allowed them to
self-pollinate
ď¨ F were a mix of tall
2
and short
ď¨ Âž were tall and Âź
were short
8. Experiments with Other Traits
ď¨ Mendel crossed pea
plants with other
contrasting traits such as
seed shape, seed color,
seed coat color, etc.
ď¨ In all crosses the F1
generation had only 1
form of the trait
ď¨ In the F2 generation the
âlostâ form reappeared
in Âź of the plants.
9. Dominant and Recessive Alleles
ď¨ Mendelâs Conclusion
ď¨ factors control the
inheritance of traits in
peas.
ď¨ They exist in pairs
ď¨ The female parent
contributes one factor and
the male parent contributes
the other factor
ď¨ One factor in a pair can
mask or hide the other
10. Genes and Alleles
ď¨ Genes â factors that
control a trait
ď¨ Alleles â different forms of
a gene
ď¨ An organism traits are controlled
by the alleles it inherits from its
parents.
ď¨ Some alleles are dominant, while
others are recessive
ď¨ Dominant allele â trait always
shows
ď¨ Recessive allele âtrait is hidden
whenever dominant allele is
present
11. Alleles in Mendelâs Crosses
ď¨ Stem Height Cross
ď¨ P generation tall tall x short short
ď¨ F1 generation all were tall short- Look tall
ď¨ F2 generation:
ď¨ Âź tall tall - look tall
Âź tall short + Âź short tall â look tall
Âź short short â look short
12. Symbols for alleles
ď¨ Letters are used to
represent alleles
ď¨ Capital letters are used
for dominant alleles
ď¨ Lowercase letters are
used for recessive alleles
ď¨ Purebred tall = TT
ď¨ Purebred short = tt
ď¨ Hybrid (one of each) =Tt
13. Significance of Mendelâs Contribution
ď¨ Before Mendel most people thought that the traits
of an individual were a blend of their 2 parents.
ď¨ If they blended the Tt plants should be medium
height
ď¨ Mendel found out that traits are determined by
individual alleles some of which are dominant
and some recessive.
ď¨ Recessive traits may seem to disappear in the
offspring only to reappear in the next generation
ď¨ Mendelâs work was not recognized during his
lifetime, but was rediscovered in 1900. He is now
considered the Father of Genetics.